1. Field of the Invention
In general, the field of this invention lies in medicine and veterinary practice; most examples being related to the practice of medicine for the benefit of human patients, use in analogous fields of veterinary medicine to the extent applicable also being within the scope of the invention. More specifically, this invention relates to the treatment of blood and blood derivatives such as clotting factors, plasma, serum, platelets, packed red blood cells, and the treatment of other biologicals such as tissues, tissue cultures, cells, organs and products thereof to ensure freedom from disease-causing microbes.
2. Description of Related Art
The history of iodine as a disinfecting agent is long. Iodine was officially recognized by the Pharmacopeia of the United States in 1930, and clinicians and microbiologists have developed a great amount of experimental data on iodine as well as numerous clinical uses for iodine.
A number of authors have summarized the disinfecting properties of iodine and the other halogens by reviewing the literature and analyzing the existing data. Some of their most germane conclusions are:
(1) A standard destruction (i.e., a 99.999% kill in 10 minutes at 25.degree. C.) of enteric bacteria, amoebic cysts, and enteric viruses requires available I.sub.2 of about 0.2, 3.5, and 14.6 ppm, respectively. PA1 (2) On a weight basis, iodine can inactivate viruses more completely than other halogens. PA1 (3) In the presence of organic and inorganic nitrogenous substances, iodine is the cysticide of choice because it is not involved in side reactions that interfere with its disinfecting properties. PA1 (4) I.sub.2 is two to three times as cysticidal and six times as sporicidal as hydroiodic acid (HOI), while hydroiodic acid is at least 40 times as virucidal as I.sub.2. This behavior is explained on the one hand by the higher diffusibility of molecular iodine through the cell walls of cysts and spores and on the other hand by the higher oxidizing power of hydroiodate. PA1 (1) iodine reacts with the basic amino group (N--H) that forms an essential part of amino acids and also forms N-iodo derivatives with the nitrogen in nucleotide bases; these reactions alter the charge structure as well as geometry (iodine is a very large atom) of proteins and other biomolecules, thereby disrupting their functions; PA1 (2) iodine oxidizes sulfhydryl groups (S--H) of the amino acid cysteine, thereby disrupting the disulfide bridges that stabilize and determine secondary and tertiary structure of peptides and proteins; PA1 (3) iodine reacts with the carbon-carbon double bond of unsaturated fatty acids, thereby altering or disrupting lipid bilayers and generally damaging biological membranes; and PA1 (4) iodine reacts avidly with the phenolic side chain of the amino acid tyrosine, further disrupting protein structure.
Gottardi, Iodine and Iodine Compounds in DISINFECTION, STERILIZATION, AND PRESERVATION, Third Edition, Block, Ed., Lea & Febiger, Philadelphia, 1983, and the references cited therein provide more details respecting the background discussed above.
Although the exact means by which iodine exerts its disinfecting properties are not fully known, it can be assumed that the following chemical reactions are, to some extent, involved:
Despite the successes achieved with iodine, it has long been known that the use of iodine possesses a number of more or less serious drawbacks. Not only is iodine poisonous if ingested in quantity, it irritates and stains the skin and has a rather unpleasant odor. Because iodine causes considerable stinging if used to disinfect wounds and because there is significant danger of developing an allergic reaction to topical iodine applications, considerable effort has been expended to develop iodine compounds or complexes which preserve the disinfecting properties of iodine while suppressing its undesirable properties.
Iodine-polymer complexes, e.g. with polyvinylpyrrolidone (PVP) and complexes of iodine with nonionic surfactants, e.g. polyethylene glycol mono-(nonylphenyl)-ether, have been used with considerable success. However, use of these compounds in direct contact with fragile biological materials has been limited either because the killing power of iodine is dissipated in the biological material or because iodine damages the biological material.
Povidone iodine (iodine-PVP complex) is capable, under favorable circumstance, of killing all classes of pathogens encountered in human infection: both gram-positive and gram-negative bacteria, mycobacteria, fungi, yeasts, protozoa, and viruses. It has been assumed that these and similar instances of disinfection by iodine are mediated by the chemical reactions listed above.
Although damage to biological material during disinfection by iodine and iodine complexes is a serious problem, an equally serious problem is posed by the dissipation of the iodine by the biological material. That is, the very chemical reactions that result in disruption of microbes also occur between iodine and the biological materials being disinfected. Thus, iodine is consumed by proteinaceous substrates and its efficacy as a disinfectant is thereby reduced. This may be due to a reducing effect of the material to be disinfected which leads directly to the conversion of iodine into nonbacteriacidal iodide. Alternatively, free iodine may be consumed in the various organic reactions mentioned above. Thus, not only is the reservoir of available iodine diminished, but the equilibrium of triiodide may also be influenced as well since an increase of iodide results in more molecular iodine being converted into triiodide. This results in a decrease in the concentration of free molecular iodine, the actual antimicrobial agent.
On the other hand, when povidone-iodine preparations are mixed with liquid biological materials (e.g. blood, etc.) there is, in addition, a dilution effect characteristic of povidone-iodine systems which actually results in an increase in the equilibrium concentration of free molecular iodine. To what extent the latter effect compensates for the other two effects depends on the content of reducing substances.
When povidone-iodine is mixed with whole blood, a marked decrease in the concentration of free molecular iodine occurs, while, when mixed with blood plasma, the iodine concentration remains practically unchanged. Durmaz et al., Mikrobiyol. Bul. 22(3), abstract (1988); Gottardi, Hyg. Med. 12(4): 150-54 (1987). Presumably, the abundant proteins of the cellular constituents of blood are more reductive and contain many more iodine reactive sites than do the soluble proteins of the plasma. This result may be slightly at odds with the well known fact that albumin (a major plasma protein) is particularly effective in reducing or totally inhibiting the biocidal power of iodine.
The current inventor has explored the use of iodine complexes in the treatment of blood and blood complexes in considerable detail. For example, the inventor's U.S. Pat. No. 5,370,869 discloses a method of disinfecting platelet-bearing liquid by contacting the liquid to be cleansed with solid povidone-iodine to expose the platelet-bearing liquid to iodine and thus kill pathogenic organisms therein, and thereafter removing the liquid from contact with the solid povidone-iodine.
Additional aspects of the inventor's work are reported by Highsmith et al., Blood, 86(2): 791-96 (1995). This study explored the use of liquid iodine for inactivation of several lipid and nonlipid enveloped viruses in an antithrombin III (AT-III) concentrate. Iodine at levels of about 0.01% to about 0.02% caused between 43% and 94% loss of AT-III activity, as well as degradation of AT-III as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis.
However, addition of up to about 0.1% human albumin protected the AT-III against both inactivation and fragmentation. At albumin levels sufficient to retain greater than 75% of AT-III activity, more than 1.times.10.sup.6 sindbis, encephalomyocarditis, and vesicular stomatitis viruses, more than 1.times.10.sup.4 of pseudorabies, and more than 1.times.10.sup.3 of human immunodeficiency virus were inactivated. Except with sindbis virus, this represented complete inactivation of all the viruses spiked into the AT-III concentrate.
The numerous references cited in the above-identified patent and research publication, of which the present inventor is a coauthor, and which describes results of tests using his concepts and methods, provide in-depth discussions of the background technology, to which the reader is referred. These disclosures are incorporated herein by reference.